1. Field of the Invention
This invention relates to force or pressure measuring devices, and more particularly to a clamp that measures force applied by the clamp with an improved degree of precision.
2. Description of the Related Art
The need for measuring the force or pressure while clamping two parts together or while bonding sensors to a substrate can be critical. Many parts and sensors are pressure sensitive and can fail under too much load. Many manufacturers of adhesives and sensors recommend a specific pressure (force) while bonding two parts together or while bonding a sensor to a substrate.
Making the actual measurement of the force being applied can be very cumbersome at best due to the need for additional load sensors and load indicating equipment. Prior methods for measuring the force were by use of load washers or miniature load cells in combination with load indicating equipment. Calibrated spring clamps have also been used. Load washers and miniature load cells add an additional part in the load path that can add to the destabilizing effect of the loading mechanism. Additionally, they require an external power source and load indicating equipment to obtain the force. Spring clamps can lose their calibration quickly by the weakening of the springs, and they are limited to the force that the spring can produce determined by its size.
Additionally, attempts have been made in the art to achieve force measure clamps with a varied degree of success.
U.S. Pat. No. 5,666,964 to Meilus is directed to a C-clamp type muscle treatment device that has a pressure measuring strain gage to record pressures at which the patient reports discomfort. A muscle clamping tool 10 in two embodiments shown in FIGS. 1 and 2 has a pair of opposed jaws 12 and 14 that can be brought together gradually for applying pressure to muscles. When pain is felt, a reading can be taken from the display 31 of the pressure read by the strain gage 30. Handle 18 is a quick release device that can instantly be activated to release the jaws.
U.S. Pat. No. 4,549,355 to Sauer, deceased, et al. is directed to a strain gage device for determining with accuracy the stem size of a plant without damaging it. Consequently, the strain gage device is acting as a micrometer rather than as a clamp. A dendrometer 10 includes a C-shaped transducer member 15 having a pair of elongate jaws 20, 21 for engaging a plant stem 12 with the jaw 21, having an adjustable connection 24 by means of an adjustment pole 25. Mounted on the transducer member 15 is a flexible transducer 14 comprising a bridge of strain gages R1-R4. When the stem changes in size, the changes in the relative amounts of tension or compression experienced by the strain gages can be interpreted to give an electronic indication of the diametrical size of stem 12.
U.S. Pat. No. 4,911,004 to Leon is directed to a portable clamp means in several embodiments that has strain gages that can determine axial loads on a cylindrical member that the clamp is applied to. The axial load on a cylindrical member 12 can be determined by the system that includes a C clamp device 10. The device includes a clamp means 14 and a strain gage sensor means 16 that together constitute a diametral strain-measuring device. The system includes a computation means 17 connected to the sensor means 16 and can include a storage and display means.
U.S. Pat. No. 3,535,937 to Wiggins et al. is directed to a pipe pressure measuring apparatus in the form of a C-shaped clamping means that has a plurality of strain gages for determining the pressure in a pipe by measuring the strain that results from the expansion of the pipe when under pressure. The apparatus 22, generally a U-shaped one-piece body, has inserts 30, 32 that are positioned in slots and face each other with curved inner surfaces that are complementary to the surface of the pipe being measured. A screw 54 threaded into a bore 50 provides a clamping means for the two inserts. Strain gages 70, 72, 74 are mounted on the body and connected to a strain indicator 84 which will provide a visible reading which can be translated into an internal pressure after suitable calibration of the apparatus.
U.S. Pat. No. 3,965,745 to Carey is directed to a pressure-responsive transducer that fits a fluid-carrying pipe or conduit and uses strain gages to determine the force and therefore, the pressure within the pipe. The housing element or yoke 11 has a slot 13 housing a ball bearing 15 and a pair of bolt-like members 25, 27 that adjustably position ball bearings 37, 39. A piezoelectric crystal 49 is secured to the housing element 11 so as to produce a voltage signal when the housing element 11 bends providing a signal in response to fluid surges in the conduit.
From the art, it can be seen that some prior clamps or force measuring devices seek to measure an initial force but generally do not seek to apply such force for clamping purposes. Consequently, such clamps cannot be used as clamps as for attaching one item to another by adhesive. While such prior art devices are clamp-like in shape, they do not perform the same compression functions as a clamp and the use of the term xe2x80x9cclampsxe2x80x9d in such devices indicates their appearance but not their operation as such devices do not clamp two things together with a selectable force or pressure.
The purpose of the force-measuring clamp of the present invention is to give the user a force indication or reading of the force being applied to the parts being clamped. The design of the force-measuring clamp is such that it can be implemented with almost any size clamp and measure almost any reasonable magnitude of force.
Preferably, a full bridge strain gage circuit is installed on a clamp and incorporates span and zero circuits with the output fed into a digital display. The strain gage is connected to the clamp and measures minute elastic deformities arising when the clamp applies force to an object. The design is simple, compact, and practical for many applications. Using a unique circuit design coupled with advanced engineering techniques, a precision clamp is achieved that allows the accurate application of force or pressure to a system such as two delicate electronic parts that are subject to compression while an adhesive sets.
It is an object of the present invention to provide a clamp that clamps or holds objects together or clamps or holds a single object.
It is another object of the present invention to provide a clamp that is capable of indicating the force that it is applying.
It is yet another object of the present invention to provide a clamp that is subject to calibration for both a non-loaded state (where no force is applied by the clamp), as well as a loaded state (where force is applied by the clamp).
It is yet another object of the present invention to provide a force-measuring clamp that is generally compact, easily calibrated, precise and accurate.
These and other objects and advantages of the present invention will be apparent from a review of the following specification and accompanying drawings.